Many kinds of laser sources have been developed in the past and are presently available in the market in order to satisfy various needs in the field of industrial processes and in particular in the field of processes on metal materials. In general, different processes (such as welding, brazing and cutting of metal materials), different degrees of precision in the process and different characteristics of the materials being processed (such as a different values of the thickness of a metal sheet to be welded or to be cut) require different characteristics of the laser beam in order to ensure optimum results. For some of these processes, the quality level of the laser beam may be lower, whereas for other applications the quality of the beam must be higher.
In the present description, and in the following claims, by the term “quality” of the laser beam means the ability of the laser beam to be focused into a very small spot, so as to give rise to a high power density at the laser spot. The quality of the laser beam defined in this manner is commonly represented by the value of a parameter called BPP (“Beam Parameter Product”), measured in millimeters per milliradiant (mm.mrad) corresponding to the product of one half of the divergence angle of the laser beam by the beam diameter at its narrowest portion (beam waist). The quality of the laser beam is higher when the value of BPP is lower. Therefore, different industrial applications may require the use of laser beams with values of the BPP parameter much different from each other. Similarly, also the power of the laser beam may be varied, as a function of the specific applications.
In many laser sources of known type, it is possible to vary the quality and the power of the laser beam to a very limited extent, with no possibility however of modifying the characteristics of the laser beam significantly. For this reason, at present it is often necessary to use different laser sources for performing different industrial operations.
On the other hand, it would be desirable to have a single “universal” laser source, which may be easily adapted depending upon the nature of the industrial operation to be performed and/or the nature of the materials to be processed.
Among the various types of laser sources which have been already developed and are presently available on the market, diode laser sources and laser sources with active optical fibres are worth to be mentioned here in particular. The latter type comprises optical fibres in which an “active” material is dispersed (typically a rare earth material) which has the ability of amplifying a light beam by exploiting the principle of stimulated emission. Typically the active optical fibre is “pumped” with a laser beam generated by a diode laser source. In general, sources with active optical fibres generate a higher quality of the beam with respect to diode laser sources, while causing a loss of power due to the dispersions within the optical fibre.
FIG. 3 of US 2014/0177038 shows a laser device with dual brilliance, having a fibre-integrated optical beam switch, able to switch the laser beam between two optical fibres, one of which is connected to a first outlet, the other optical fibre being connected to an ytterbium fibre oscillator, which provides a fibre output with a radiation having a higher brilliance.